Structure and method of operation of heating furnaces



Sept. 2, 1924. 1,506,840

R. B. KERNOHAN ET AI.

STRUCTURE AND METHOD OF OPERATION OF' HEATING FURNACES Filed Der;H 8, 192! 6 Sheets-Sheet l sept. z 1924. 1,506,840

R. B. KERNOHAN ET AI.

STRUCTURE AND METHOD OF OPERATION OF' HEATING FURNACES Filed Dec. 8A 1921 6 Sheets-Sheet Z lIf/// F! LEI v "if /Nve/vraeg wwf/5665s ((3 D @Mg MM@ Sept. 2 1924. 1,506,840

R. B. KERNOHAN ET AL STRUCTURE AND METHOD OF OPERATION 0F HEATING FURNACES Filed Dec. B 1921 6 Sheets-Sheet 3 Sept. 2 1924. 1,506,840

R. B. KERNOHAN ET A1.

STRUCTURE AND METHOD 0F OPERATION OF HEATING FURNACES @l/mw Sept. 2 1924.

R. B.I(EF2BH3F1ATQ E1'AL STRUCTURE AND METHOD 0F' OPERATION 0F HEATING FURNACES Filed Dec. 8, 1921 6 Sheets-Sheet 5 Wl TNGSES Sept. 2 1924. 1,506,840

R.3.i(EFUC)FhPI ET'IL STRUCTURE AND METHOD 0F OPERATION 0F HEATING FUHNACES Filed Dec. 8, 1921 6 Sheets-Sheet 6 /N VENT-0R 5? QoL/5ML tion,

line I-I, Figure II, of an open-hearth steelV` Patented Sept. 2, 1924.

UNITED STATES PATENT OFFICE.

STRUCTURE AND METHOD 0F OPERATION 0F HEATING FURNACIB.

Application 110|! December 8, 1921. Serial No. 589,023.

To all whom it may concem.'

Be it known that we, RoBERr B. KERNo- HAN, JAMES S. LooHHnAD, and WILLIBALD INns, residing at Pittsburgh, in the county of Allegheny and State of Pennsylvania, all citizens of the United States, haveinvented or discovered certain new and useful Improvements in Structure and Method of Operation of Heatin Furnaces, of which improvements the fo lowing is a specification.

Our invention relates to improvements in the structure of and in the method of operation of heating furnaces. It includes improvements upon the disclosures of an application of two of the present applicants, Kernohan and Lochhead, for United States Letters Patent, filed October 29th, 1920, Serial No. 420,377. This application is in part a continuation of our application filed October 1, 1921, Serial No. 504,640.

Our invention, as in the sequel will appear, is applicable generally to heating furnaces and their operation, but we shall first describe it in the particular application in which we have developed it, the application, namely, to an open-hearth steel furnace.

In the accompanying drawings, Figure I Yis a View in approximately horizontal secon the plane indicated by the broken furnace, in which, and in the operation of which, our invention is present and may be carried out. Figure II 1s a view in vertical Asection of the same furnace, on the lane in= dicated by the broken line II-II, igure I. Figures III and IV are views corresponding te Fi ures I and II and illustrating certain modifications of the invention. Figure V is a fragmentary view, corresponding to Figures I and III and illustrating further modification. Figures VI, VII, and. VIII are views1 in vertical section, VI and VIII through ingot heating furnaces, VII through a billet heating furnace, and in these figures the applicability of our invention to these furnaces, various in kind, is illustrated. Fig. IX is a view in longitudinal section and to much larger scale of a certain nozzle, which we preferably employ, as hereinafter Vexplained.

Referring first to Figures I and II, the furnace includes the usual hearth 1, upon which the charge is borne and where the essential refining operation takes place. Producer gas,

preheated in the regenerator (not shown) ows through passageway 3; thence it rises through vertical passageway 6, and enters from the rear the medially arranged downwardl inclined tunnel port 4. Through this rt t e stream of gas is carried into the urnace chamber. Atmospheric air, preheated in the air regenerator (not shown), flows through passagewa 2; thence it rises in divided flow througli two vertical passagewage 7 and 8, symmetrically arranged one on ext er side of the mid-line of the furnace, and enters from the rear the downwardly inchned port 5, over-arching port 4. Through this ort air is carried into the furnace cham r. Duets 9 and 10 lead from air passageways 7 and 8 and open into port 4. Of these ducts it is to be observed that they are symmetrically arranged and that the flow t rough them will be symmetrical with respect to the mid-line of the furnace; they extend obliquely forward, and the streams flowing through them will converge with the stream flowing directly through the tunnel port 4; they open into the tunnel port 4 at an intermediate point in the length thereof, and the conver ing streams will min le before 'the mout of the port is reac ed. Nozzles 19 and 20 are provided, through which compressed air from a supply pipe 21 may be blown in jets forwardly throu h ducts 9 and 10. In supply pipe 21 is a va ve 23 for regulating the fiow, and con,- veniently a second valve 22, for cutting off the flow entirely.

The showing afforded in Figs. I and II will be understood to be diagrammatic, and particularly in these respects :-The ducts 9 and 10 are shown as rectangular in cross section and uniform in dimensions throughout their extent. Manifestly they may be particularly shaped accordin to the teaching of pneumatics, to afford in ighest degree the effect described; the nozzles 19 and 20, shown diagrammaticallyas mere tapered terminations of the feed pipes protruding into the ducts, may be elaborated and refined in form; they may be made of the multi le-jet type; they may in osition be so related to the form of the ucts as best to achieve their effect; again, the openings through the walls of passageways 7 and 8, through which the nozzles 19 and 20 are shown to be movable are, in order that the structure may be clearly understood, shown diagrammatically as Tater in dimensions than in actual building e pause to remark that the s mmetry of the arrangement here describe is a preferred but not a limitingl feature.

We have just said of t e nozzles 19 and 2O that the may be elaborated and refined in form. nd here we pause and anticipate a description of mode of operation to remark that 'ets of com ressed air are projected longitu inally in ucts 9 and 10 at the intake end of the furnace to induce ow of streams of air from u take passageways-'I and 8 through these ucts 9 and 10 and into port 4. Our further and more s ecific invention in res ectto these ducts 1s illustrated in Fig. I where we show a nozzle of a conver entdiver ent shape, sometimes called a De aval nozz e. Inspection of Fig. IX will in view of the foregoing statement make plain the feature here (dwelt upon.

The convergent-divergent nozzle has this capacity,that if gas under pressure exceedin a critical minimum (for air this critica minimum is a pressure of approximately two atmospheres) be jetted through it, a very high jet velocity may be attained. From an ordinary convergent nozzle jet velocity is limited to the velocit of sound in air,about 1,100 feet a secon From a convergent-divergent nozzle jet velocities of 1,500 feet a second and even higher may be goThe advantage of this high-velocity nozzle to our invention is thls: If the comressed air jette-d through nozzles 19 and 20 e unheated it will on mixing with the air drawn from passageways 7 and 8 effect some coolin of the streams, and there is a oint beyon which such cooling may not a van` tageously be carried. On the other hand, it is an economic advantage if the air jetted from the nozzles may be used in unheated condition. Increased velocity of et means that the same flow of heated air rom assageways 7 and 8 through ducts 9 an 10 may be got with jets of iminished volume. Accordingly, the employement` of convergent-divergent nozzles means that we can use unheated air under conditions which otherwise would require preheating,-pre heating, that is, of the compressed air jetted from the nozzles.

In certain of the ensuing claims we use the phrase high-velocity jet of as. By that phrase we designate a jet of t e character here defined,-a jet, that is to say, ex-

'ceeding in velocity any jet which may be forced from an ordinary convergent nozzle, and such as may be delivered from a convera gent-divergent nozzle, as described. We have shown the compressed air supply pipes 21 at opposite ends of the furnace,

together with t e connections which ternminato in nozzles 19 and 20, to be sus ed as by chains 24, and it will be un erstood that by such means the nozzles 19 and 20, itioned as shown at the intake (left and) end of the furnace, may at the outtake (right hand) end be swung aside, away from the deleterious influences of the outilowing products of combustion. As an alternative ex edient, these pipes may be stationa an the nozzles water-achetedan expe ient so well known in t e general field of furnace structure as to require nno illustration. n

As shown in the-drawings, the furnacereversing vinstrumentalities will be understood to be arran d for the inow of gas and air at the leftand end and for the outflow of products of combustion at the righthand end. At the left-hand end of the furnace the valve 22 in the suppl pipe 21 will be understood to be open am;I at the ri ht hand end the corresponding valve wil Ybe understood to be closed, and at that end the pipe itself is shown to be retracted and the nozzles 19 and 20 withdrawn be ond the walls of vertical passageways 7 an 8. Gas and air are entering through the ports at the left-hand end and are burnin in a flame which sweeps from left to rig t, and the products of combustion are escaping throu h the ports and passageways at the rightand end. At proper intervals of time the furnace is reversed and, incidentally to reversal, the ipe 21 and nozzles 19, and 20 at the rightand end which had been retracted are advanced, those at the left-hand end which had been advanced are retracted. Valve 22 of the advanced pipe 2l is opened, while the corresponding valve in the retracted pipe has on retraction been closed. (Apparatus for effecting reversal of the furnace requires no illustration, and we have not sought to aiord illustration of it.) The degree of opening of valve 23 may, if desired, be diminished as operation upon a given furnace charge progresses, to the en that at the beginnlng the flame may be relatively short and shar and toward the end relatively long and az.

In the peration of openearth furnaces as common y conducted hitherto, the draft through the furnace has been relatively feeble, and combustion has been imperfectly controlled. This has been particularly true of furnaces fired with producer gas, In the operation of these furnaces the air ordinarily has been drawn through the air regenerators and into the furnace merely by the stack effect of the regenerators and the uptakes. The gas flowing from the producer and through the as regenerator and thence to the furnace as been commonly subjected only to such pressure as is incident to its delivery from the producer. In some cases a blowing fan has been placed in the 'stream of the air supply to the furnace, but there is a ractical limitation upon the building up of) the pressure there. Nhen the pressure exceeds a small amount, leakage through the masonry of the furnace structure becomes too great. It is difficult, because of expansions and contractions incident to service, to build a furnace which shall be tight a ainst such leakage, and there is another ifliculty to be dealt with. High pressures and high velocities, ver desirable in order to produce a sharp ame, require that the ports be relatively narrow, and narrow ports do not afford at the dischar end of the furnace unhindered exit for t e products of combustion. (It is of course to be understood,and the condition has already been alluded tor-that in ordinary open-hearth operation the flow of the flame is periodically reversed, and duplicate sets of orts at opposite ends of the furnace serve a ternately to lead in the gas and air -and to lead` out the vastly greater volumes of hot products of lcombustion.) Because of these diiculties chiefly, and in spite of various relief projects, open-hearth operation as a matter of practice has been limited to low rates of flow of air and of gas and to the generation of a consequent l-ong and lazy Hume. This flame is still burning when it reaches the ports at the outgoing end of l the furnace and combustion continues through the ports and even down into the re enerators-a state of things both wasteful and destructive. A proposal to use dampers for reducing the effective size of the passageways at the intake end of the furnace, with the end in view of increasing there the velocity of flow, involves complication of structure, and the dampers, when present, absorb a reat deal of heat.

In the furnace 0% Figs. I and Il, while operation is in progress, compressed air is blown through nozzles 19 and 20 into ducts 9 and 10. This compreed air may, as has been explained, be preheated or not, as found desirable or convenient, and if preheated, the preheating may be carried to any desired degree. But, as We have explained, the necessity for preheating may Within wide limits be avoided. The jets of air issuing from the nozzles have high velocityfrom 600 to 1500 feet per second or more,- a matter conditioned upon the actual pressure of the supply and upon the shapeof the nozzle and the size and shape of the orifice. This high-velocity jet entrains hot air from the uptake passages 7 and 8, and induces a How of air through ducts 9 and 10 into the stream of gas advancing through port 4. Thus the entering stream of air is divided; one portion is directed into port 4, where it niingles with the gas before entering the furnace chamber: the other portion Hows unmingled through port 5 into the furnace -able and responsive to the degree of op '9 and 10 into The relative value of these two the stream of entering air is variening of regulating valve 23,; if that valve be closed completely, all of the air will, under such conditions as furnace chamber through port -and, indeed, because of the fact that-usually the gas advances to the furnace under pressure greater than that of the air, there will be some back fiow of gas from port 4 through ducts 9 and 1() and into the streams of air advancing to port 5. As valve 23 is gradually opened, such back flow of gas first is stopped, and then streams of air are directed forwardly through ducts 9 and 10 into the stream of gas in port 4. These streams of air increase in volume, and the streams fiowing to port 5 correspondingly decrease, as valve 23 is opened wider. Ordinarily from one twentieth to one sixth by weight of the air flowing in ducts 9 and 10 is that which flows from the nozzles; the rest is drawn in from the streams of air rising through uptake passages 7 and 8. By properly proportioning in size ports 4 and 5, passageways 7 and 8, and ducts 9 and 10, it is possible by the means described to divert through ducts port 4 any desired fraction of the streams of air rising through uptake passageways 7 and 8. Indeed, it is possible so to divert substantially the whole of these streams; ordinarily it is not desirable in operation to go so far as that, but it is referable to allow some air to enter the urnace through port 5.

When valve 23 is nearly closed the flame is long and lazy-such a flame in fact as is usual in open-hearth operation as commonly conducted hitherto; if the valve 23 is opened Wide, the flame is short and sharp. Any desired sharpness of fiame may be obtained by movement of the regulating valve 23. A shorter sharper flame than that usual in the open-hearth operation tion is then completed within the furnace chamber, Where alone combustion is desired, and the passageways and regenerators through which the outflowing gases pass are not subjected to the destructive action of combustion in progress `within them. Furthermore, regulation by valve 23 makes possible variation in uality of flame (if such variation be desired) according to the progress of the refining operation; at the beginning of a run the flame may be relatively short and sharp, and toward the end relatively long and lazy.

As has been intimated, we do not intend ordinarily to resort to special means for building up pressure on air or gas on the intake end of the furnace nor to special means for drawing the products of combustion out from the outgoing end. Nevertheless, the practice of our invention does not forbid the chamber. portions of usually obtain, enter the is desirable; combus' use of such ancillary apparatus, if for any reason it be found desirable.

The streams of air enterin port 4through ducts 9 and 10 produce com ustion in port 4, to the extent that the air and gas mix. Mixture, however, is not complete until the gases have just left port 4 on their way to the furnace. In consequence, combustion in and just beyond the opening from port 4 is so rapid that an extremely hi h temperature is attained, in spite of the injection of cold or sli htly preheated air through nozzles 19 an 20.

The projection of streams of air at relatively high velocity through ducts 9 and 10 and forwardly into port 4 effects an increased flow of gas, and that without an otherwise reipisite mcrease of plressure in the gas u ta e'passageway 6. he jet of air under igh pressure projected from the nozzle into the duct has great kinetic energy, and entraine or induces the flow of large weights of air (live to twenty times greater than issue from the jets) from the air passageways 7 and 8 through ducts 9 and 10 into port 4. Furthermore, by the use of the jets of compressed air, this projecting of streams of air through ports 9 and l0 is attained without subjecting the furnace structure to augmented pressure in the re enerators or in the air uptake passageways and 8, and without resort to dampers.

We have consistently spoken of the substance projected through nozzles 19 and 20 as compressed air, and ordinarily compressed air will be best; air is requisite to combustion in ordinary practice, and is one component of the combustible mixture Within the furnace chamber. But manifestly the jet might be constituted of some other {luidof steam, for example, or of oxygen, or of a substance which, while not entering into the act of combustion, still serves mechanically, to divert the substance of one of the two streams through the ducts 9 and 10 into the other stream.

The arrangement of ports and passageways might be reversed, and gas rising through passageways 7 and 8 diverted and projected into the air advancing from passageway 6 throu h port 4.

The furnace i ustrated in Figures I and II is designed for the use of gas as fuel and, s ecifically, producer gas. Fi and I illustrate a furnace in whic various fuels and fuel mixtures may be employed. The general structure will be understood from what has gone before, and we shall describe those features only in which dilferences are found from the structure of Figs. I and II.

The fuel port 104 is in this instance fed, not through an uptake from a regenerator, but through fuel supply pipes 25, 26, and 27. Liquid-fuel pipe 25 opens into port 104 on res III4 the-midline of the furnace from the rear, while a (pair of op osite and symmetrically arrange from o posite sides. Li uid fuel will ordinarlly introduced un er pressure. Gaseous fuel may be introduced under pressure or may be sucked in. Fuel of the character indicated introduced through pi e 25 alone, or through pipes 26 and 2 or through all three ipes, enters the streams of air which, impe led by jets issuin from nozzles 119 and 120, converge in an swee through port 104, and the fuel so introdu into the streams of air is carried by the4 streams and is mingled with the air, and so the desired combustible mixture is formed. The flame springs from port 104 and, as the burnmg stream advances, the flame is nourished by supplementary streams of air entering the furnace through port 5. l

The particular nature of the liquid fuel entering throu h ipe 25 may be such as is convenient an a equate, but-particularly where at the same plant with the openhearth furnace a b -product coke plant is found-tar is availa le as a by-product, and its use in our furnace becomes a matter of convenience and economy. In place of tar. fuel oil may be used, or some other liquid fuel. This liquid fuel will be fed in under head or ressure. When tar is used, it is preheate and introduced under high pressure. The gas introduced into port 104 throu h pipes 26 and 27 may be artificial gasrom the same by-product plant, for example, as the tar-, or xt may be producer gas of the water-gas t pe, or some other artificial gas, or it may natural gas. We do not contemplate, in the case of this furnace of Figures IIIand IV, a pre-heating of the gas by regenerator or otherwise, and, although we do not limit ourselves to the use of gas of an particular quality in matters of combustlbllity and heat units.' still (if high tem eratures are to be obtained) the gas shoul be a relatively rich gas. As we have said, we may, in the operation of our furnace, use tar alone as fuel, or gas alone, or we may use both, the one in substitution for the other, or by way of augmentation the one of the other, or we may regularly use both as substantial and permanent components of our fuel sup ly. Of course the rate of flow of liquid fuelJ to ort 104 and the volume and the pressure o the gas supply may be controlled b ordinary means, a showing of which is eemed unnecessarfy. y'

One urther specification regarding fuel may here be made. Powdered carbonaceous material, commonly powdered coal, carried on a stream of air or other as is a known fuel, artaking lar ly of t e character of llui fuel,-notablge 1n that it may be carried by a pipe am? delivered in a gaseousuel pipes 26,' 27 open lll) stream. We mean in our include such fuel under fuel."

The nozzles 119 and 120 are in this case (Figs. III and IV) so arranged that they project their jets across passageways 7 and 8 and into the ends of ducts 109 and 110.

In operation of the furnace of Figures III and IV, the notable difference from that of Figures I and II is in the fuel intended to be used. The fuel is fiuid and may be gaseous or may include a aseous carrier and if gaseous, while it may the expectation is that ordinarily it will notl be, preheated. The fuel pipes at the outgoing end of the furnace will be understood to be closed. At the inlet end the fuel pipes 25, 26, 27, or so many of them are to be used (according to the description given above) are open. The streams of air impelled by jets from nozzles 119 and 120 and flowing through ducts 109 ensuing claims to the term fluid and 110 and thence through port 104 into the furnace chamber take up the fuel which enters port 104, form with the fuel a combustible mixture, and then advance liaming into the furnace chamber. The other portion of the air tsupplied Hows unmingled through port 5 to the furnace chamber, and there nourishes the flame. We do' not mean to limit ourselves to particular pressures, but ordinarily in the operation of the furnace of Figs. III 'and IV under the draft conditions usual in open-hearth operation, a suppl through nozzles 119 and 120 of compresse air under a pressure of from 20 to 40 pounds will be found adpquate.

The showing afforded by Figure V is in all respects the same as that of Figure III, with the following exception the nozzles 219 and 220, instead of being arran d on the farther side of passageways 7 an 8 and delivering their jets across those passageways (as shown in Figure III), are arranged to deliver their jets within ducts 209 and 210. The arrangement in this respect is similar to that of Figure I. A refinement of operation is consequent u n this arrangement. The primary notion for which these ets are provided is that already described,to impel fiow of air throu h ducts 209, 210 into port 204. A secondary function is this: Compressed air (or equivalent fluid) ma be projected from nozzles 219 and4 220 at t e outgoing end as well as at the intake end of the furnace and inconsequence a pressure condition may be built up in the port 204 at the outgoing end, sulicient to partially or completely prevent ingress of the products of combustion to the port 204, and paage thence throu h ducts 209 and 210. Correspondingly, 51e products of combustion will pass out through port 5, and port 204 and the connected parts will be relieved of the erosion and dele- .lieating furnace for ingots, the familiar terious effects of the sweep of outgoing Figure VI shows diagrammatically a furnace provided at a blooming mill. Lln it ingots I are shown resting on the hearth 301 of the furnace chamber. Furnaces for this purpose are ordinarily regenerative furnaces and admit of a considerable latitude in structure and considerable modification in mode of operation. The furnace shown will however serve as a typical furnace of this general sort. In this particular instance it will be observed that it is the air only which is re nerated in regenerators 30, while the fuel which in this instance will be understood to be gas relatively rich, in quality--coke-oven gas, for instance) is introduced through pipe 3l into the stream of regenerated air as it advances to the furnace port. A structure is built upon the wall of the passageway from regenerator to furnace port which in mill parlance is called a doghouse Within this doghouse, as clearly appears, is formed a byass 32, through which a fraction of the atlifancing stream of air is shunted. Into this by-pass open fuel-supply pipes 327 (the number and arrangement may be such as desired, ordinarily the arrangement will be symmetrical with respect to the line of flow). The fuel introduced may be liquid or gaseous, or fluid within the definition given above), or diferent pipes may bring in different fuels,

and the fuel may be introduced under res-l sure or by suction-all of these matters ave already been explained in connection with the furnace of F1 III and IV, and what is there said is appliable here. Pipe 319 carries comdpressed air (or equivalent fluid). It exten s into the b -pass 32, and from it a jet is projected in t e line of flow through e by-pass and in the direction of the furnace chamber and such jet serves, as in the other cases already described, to im el How through the by-pass and through t e ort, into the furnace. The structure differs rom the structures of Figures I to V, inclusive, in that the jet-impelled branch of the stream reunites with the other branch, and the united stream enters through the single port into the furnace. This is a variant which may be noted in passin We have said that a gas of relative ric ness will in ordinary contemplation be introduced through the fuel-suppl pipe 31 at the inlet end of the furnace. llhis gas may be natural gas, for example, or coke-oven gas, or even producer gas. From what has gone before the operation will be fully understood.

Figure VIII serves merely to indicate how the same essential invention may be applied to an ingot-heating furnace in which both air and ,gas are regenerated and rise through uptakes 307 and 306 to the furnace ort. No labored explanation is needed. he structure and operation will be understood from what has already been said.

Figure VII shows a billet fumace of familiar construction. Upon the furnace wal is built a doghouse into which doghouse there o ens an u t passageway 407 for air, which it wi be understood may lead from a recuperator or from a re nerator. lo The chamber 404 within the dog ouse, so supplied with air, opens iw the furnace chamber. Into chamber 404 fuel is introduced, as is indicated at 427, and nothing more need be said about fuel than to rel5 mark that fuel of any preferredgcharacter may be introduced in the manner and by the means alreadyx described. compressed-air pipe 419 disc arges a jet in the line of flow of air through the chamber furnace chamber. i

Mention of a recuperator gives occasion to note a further advantage of our invention. A recuperator is a heat exchan r in which streams of entering air or "gas and 26 of outi'lowing flaming gases or ot products of combustion flow 1n contiguous assageways, se arated by a heat-penetrab e partition wa This wall ordinarily is a thin wall of brickwork. Draft through' the fur- SQQna-ee is ordinarily maintained by a stack; and in the recuperator, while the stream of air flowing on one side of the partition is under a pressure slightly in excess of that of the atmosphere, the stream of hot gas flowing on the other side of the partitlon is, in co 404, and into the nsequence of the draft condition established by the stack, under a pressure t ap reciably less than atmospheric. A thin wa l of brickwork is liable to deterioration and leakage, and, with inequality of pressure on its o posite sides, leakage means disturbance o draft through the furnace chamber and loss of eiiicienc It should be understood that, heretofore, it has been impossible to suck the preheated air Aout of the recuperator except by its own buoyancy which, in some cases, has been au ented by the action of a fan at the cold air inlet of the recuperator. In any such case there is a pressure greater t an atmospheric either throughout the whole length of the air passageways in the recuperar/or, or at least in t at portion nearest to the hot-air outlet. The apgication of our invention now fully descr-i to a furnace whose air supply is preliminarily heated in a recuperator achieves a proper firing of the furnace without the attendant necessity of an unbalancing of ressures in the recuperator; the suction e ect of the jet in the air assageway leadi to the furnace is to r uce the pressure o the entering air in the recuperator to substantially that of the products of combustion flowing out through the l ures VI, VII and VIII recuperator to the stack. Consequently, wear and tear does not bring about that loss in efficiency just pointed out.

In describing the structure of ithese Figwe have said, generally, that the jet is ordinarily of compresse air, and it ordinarily will be, but it is to be understood that we are not limited to the use of compressed air, in view of what we have already said, our invention is embodied in the rovision of a jet of fluid. With this brief enition of parts, it is believed that the structure and operation of the furnace of Figure VII also will be clearly understood. 4

All that was said with reference to the furnace of Figs. I and II concerning variations in and refinements of structure; concerning the nature of the fluid projected from nozzles 19 and 20, and concernin its pressure and temperature, and the e ects of variation in these matters; all that was said concernin and means o maintaining them, will be understood to be a plicable to the furnaces of Figures III- III and their operation, What has been said concerning pressure and temperature of fuel will be understood to be a plicable generally in the operation of the urnaces described.

Reviewing the structures of all of the figures, it will be seen that there is throughout a chamber which, varying in detail, possesses constant characteristlcs. We allude to the chamber 4 of Fi res I and II, 104 of Figures III and I 204 of Figure V, 304 of Fliures VI and VIII, and 404 of Figure V In the ensuing claims we use in some cases the term port, in some cases the term mixing chamber. It will be understood that t e varying phrase merely lays emphasis upon certain characteristics of this same structural element, and neither term is used in an specifically limiting sense.

We have i ustrated a considerab e latitude in modification of structure, and in method of operation. In so doing we have not intended to limit the range of permissible latitude, but to indicate rather that the ield is wide within which our invention may be practiced.

We claim as our invention:

1. In a heating furnace using preheated air for combustion the method of operation herein described which consists in maintainlng a passageway for such preheated air leading to the furnace chamber and in ro- ]ecting into such passageway a flow-in ucing et of compressed gas at a velocity exceedlng that of sound and causing fuel to mingle in the stream.

2. In the operation of a furnace usin preheated air for combustion the meth erein described of impelling the flow of air draft conditions maintainedl t0 the furnace chamber which consists in projecting into the line of flow a jet of gas at a velocity exceeding that of sound.

3. The method herein described of developing a flame in a heating furnace which consists in impelling under jets of Huid a plurality of streams of air into confluent entrance into the furnace chamber, and projecting into the confluent streams a supply of liquid fuel.

4. In a heating-furnace structure the combination with a furnace chamber of an air passageway leading thereto, means for projecting into said air passageway a flow-inducing jet of gas at a velocity exceeding that of sound, and means for admitting fuel to the induced stream, substantially as de scribed.

5; In a heating-furnacestructure the combination with a furnace chamber provided with an intake passageway for air and an outgoing passageway for products of combustion, means for drawing the products of combustion through the outgoing passageway and means for projecting a flow-inducing jet of fluid at a velocity exceeding that of sound within the intake passageway, substantially as described.

G. The method herein described of firing a furnace which consists in establishing conditions of low-velocity How through the furnace as a Whole and at. the intake end increasin(r locally the flow to a flow of high velocity by projecting into the flow a )et of fluid at a velocity exceeding that of sound.

In testimony whereof we have hereunto set our hands.

ROBERT B. KERN OHAN. JAMES S. LOCHHEAD. VVILLIBALD TRIN KS. 1Witnesses:

S. A. MCFARLAND, I. G. HIGHLY.

DISCLAIMER.

1,506,840.Robert B. l1 emitan., James S. Lochead, and Willibald Trinka, Pittsburgh, Pa Sfmucrm Asn Merrimn or OPP-.muon or Hmmm: Fonmions. Patent dated September 2, 1924. Disclaimer filed September 17, 1924, by the patentees.

Hereb enter their disclaimer- To c aims l, 2, 4, and 6 of the said Letters Patent, No. 1,506,840, the said claims reading as follows:

1. In a heating furnace using preheated air for combustion the method of operation herein described which consists in maintaining a paagewa for such preheated air leading to the furnace chamber and in projecting into snci passagewa a flow-inducing jet of compressed gas at a velocity exceeding that of sound an causing fuel to mingle in the stream.

e operation of a furnace using preheated air for combustion the method henein described of impelling the flow of air to the furnace chamber which consiste in rojccting into the line of flow a )et of gas at a velocity exceeding that 4. In n heating-furnace structure the combination with a furnace chalnbcr of an air passageway lending then-cto, iin-ans for projecting into said air passageway a How-inducing jet of pas at n velocity exceeding that of sound, und means for ndmittin fue] to the induced stream, substantially as described.

5. In a eating-furnace structure the combination with a furnace chamber provided with an intake passugewa for air and an outgoing passageway for productsof combustion, means for rawing the products of combustion throu h the outzing passageway and means for projecting a flow-inducing jet of fluid at a ve it exceeding that of sound within the intake passageway, substantially as described.' 

